/Engine/Source/Runtime/Core/Public/UObject/ScriptDelegates.h
Adds a function delegate to this multi-cast delegate's invocation list if a delegate with the same signature doesn't already exist in the invocation list
void AddUnique ( const [TScriptDelegate](API\Runtime\Core\UObject\TScriptDelegate)< [ThreadSafetyMode](API\Runtime\Core\UObject\TMulticastScriptDelegate\ThreadSafetyMode) > & InDelegate )